Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-12.co.uk. NS
Answer
awsdns-12.co.uk. 5 NS g-ns-1487.awsdns-12.co.uk.
awsdns-12.co.uk. 5 NS g-ns-332.awsdns-12.co.uk.
awsdns-12.co.uk. 5 NS g-ns-908.awsdns-12.co.uk.
awsdns-12.co.uk. 5 NS g-ns-1808.awsdns-12.co.uk.
Authority
The response has no authority records.
Additional
g-ns-332.awsdns-12.co.uk. 5 A 205.251.193.76
g-ns-908.awsdns-12.co.uk. 5 A 205.251.195.140
g-ns-1487.awsdns-12.co.uk. 5 A 205.251.197.207
g-ns-1808.awsdns-12.co.uk. 5 A 205.251.199.16
g-ns-332.awsdns-12.co.uk. 5 AAAA 2600:9000:5301:4c00:0:0:0:1
g-ns-908.awsdns-12.co.uk. 5 AAAA 2600:9000:5303:8c00:0:0:0:1
g-ns-1487.awsdns-12.co.uk. 5 AAAA 2600:9000:5305:cf00:0:0:0:1
g-ns-1808.awsdns-12.co.uk. 5 AAAA 2600:9000:5307:1000:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0